Endodontic root canal files are small files held in the fingers of the dentist or endodontist to clean out decayed and damaged material from the root canal of a tooth and to shape the canal so that the root canal can be filled and the tooth can be restored. Typically, the root canal files are tapered, often helically fluted, and provided in sets of files of progressively increasing diameter. In use, the files are inserted into the root canal of the diseased tooth and are rotated, either continuously in one direction or by oscillatory rotational motion. The files are also used by reciprocating them longitudinally. Such files are required to follow the root canal of the tooth, which is usually curved, to ream as well as remove material from the tooth, and to do so without breaking the file while it is inserted in the root canal and without removing portions of the tooth root that are advantageously retained, that is, without ledging or perforating the canal.
Examples of prior art files are disclosed in U.S. Pat. Nos. 4,299,571, 4,538,989, 4,934,934 and 5,106,298, the disclosures of which are each expressly incorporated by reference herein.
Endodontic root canal files of the prior art, particularly those having helical flutes, have a tendency to pull into or push out of the canal when rotated, or to develop twisting moments when reciprocated. This can result in bent or broken files and cause the endodontist difficulty in controlling the file and thereby enlarge the canal in an unintended direction. Such helical files have a naturally non-round cross-section, which presents a spiraling neutral axis whereby the bending and torsional axes are not collinear, resulting in unequal stress. Such files present a compromise between bending flexibility and torsional rigidity. Furthermore, when such prior art files are rotated while bent, they have a tendency to produce a whipping or snaking action, where the axis of rotation is not about the geometric axis of the instrument, thereby producing inconsistent results in the shapes and sizes among the prepared root canals. In addition, the files of the prior art perform in a manner that is a compromise between cutting efficiency and efficiency of material removal.
Accordingly, there remains a need to provide an endodontic file that overcomes or avoids the problems experienced with the root canal files of the prior art discussed above.